1. Technical Field
The present invention relates to a valve train of an internal combustion engine in which a valve operation characteristic can be changed which includes an opening and closing time and a maximum lift of an engine valve which is a suction valve or an exhaust valve.
2. Related Art
For example, Patent Document 1 discloses this type valve train. This valve train includes a transmission member having a supporting point moved by a rotatable eccentric body so that a reciprocating motion of a reciprocating valve provided in the cylinder head can be adjusted, and this transmission member is driven by a cam of the cam shaft so as to open and close the reciprocating valve. Further, in order to press the transmission member to the cam, a return lever or a return shaft, which will be referred to as a return lever and others hereinafter, acting in the transmission member is provided. The return lever and others are pushed by a compression spring supported by a guide element incorporated into the cylinder head.
[Patent Document 1]
JP-A-Hei7-63023
In this connection, in the valve train disclosed in Patent Document 1, the transmission member is driven and moved not only by the cam but also by the eccentric body. On the other hand, the guide element for supporting the compression spring is fixed to the cylinder head. Therefore, in the case where a movement of the supporting point of the transmission member is increased in order to increase the control range of the valve operation characteristic, that is, in the case where a movement of the supporting point of the transmission member is increased, for example, in order to increase at least one of the control range (change) of the maximum lift of the engine valve, which corresponds to the reciprocating process of the reciprocating valve of the valve train of Patent Document 1, and the control range (change) of the opening and closing time of the engine valve, the following problems may be encountered. Even when the transmission member is driven by the eccentric body and moved, the return lever and others are maintained in a state in which a bias force of the compression spring is given to the transmission member. In order to maintain this state, when a portion of the transmission member, which will be referred to as “an acting section” hereinafter, on which the return lever and others act, is increased in the size corresponding to the movement of the supporting point, the acting section of the transmission member is made larger in the size, that is, the valve train is made larger in the size. On the other hand, in order to avoid the increase in the size of the acting portion of the transmission portion, since it is necessary to give priority to an arrangement of the guide element, the size in the transmission member is increased and further the arrangement of the transmission member is restricted. As a result, the valve train is made larger in the size.
In the case where the movement of the supporting point of the transmission member is increased, an expansion and contraction of the compression spring are increased corresponding to the increase in the movement of the supporting point. Accordingly, a change in the bias force of the return lever and others given to the transmission member is increased. When the change in the bias force of the return lever and others is increased, it becomes difficult to press the transmission member to the cam by an appropriate bias force. Therefore, for example, the following problems are encountered. If the bias force is set at an appropriate value on the contraction side of the compression spring, when the compression spring is expanded, a sufficiently strong bias force can not be obtained. Since the bias force is excessively weak, vibration is generated in the transmission member. Therefore, it becomes difficult for the engine valve to be appropriately opened and closed. On the other hand, if the bias force is set at an appropriate value on the expansion side of the compression spring, when the compression spring is contracted, the bias force is excessively increased. Therefore, a contact portion, in which the return lever and the transmission member are contacted with each other, tends to be abraded. Accordingly, it becomes necessary to take measures for enhancing the anti-abrasion property of the contact portion, which raises the manufacturing cost. When a spring constant is set at a low value in order to suppress a change in the bias force caused by an increase in the expansion and contraction of the compression spring, the compression spring is made larger in the size.